A simultaneous Emission/Transmission Computed Tomography (ETCT) system possesses the advantages of both SPECT and CT by offsetting the individual weakness of each. However, the successful development of ETCT machine must include improved spatial resolution, which currently is limited by the X- ray and gamma-ray detector systems used. Scintillation cameras used in SPECT are essentially at their limit of spatial resolution. Silicon photodiode detectors used in CT are limited by sensitivity. The most promising detectors for this application are solid state detectors like HPGe and CdTe. The cryogenic requirement of HPGe makes CdTe a unique candidate for the ETCT innovation. Our recent process with CdTe x-ray and gamma-ray detectors is very encouraging, an energy resolution of l.7KeV FWHM has been observed for 57Co (l22KeV). Further research into this promising system has high potential of producing a new detector technology with better performance, which could be the basis for a future generation of medical imaging instruments like ETCT. The goal of this Phase I program is to demonstrate the feasibility of using the semiconductor CdTe in ETCT instruments.